The present invention relates to a folded filter material of the type formed by bending.
Such a filter material is known from U.S. Pat. No. 3,029,812. The known filter material is used as an insert in a respirator or breathing mask and consists of a web of paper that has been laid in folds. However, when a filter material is formed that has been provided with folds, the risk arises that the folds collapse, whereby the passage resistance is increased, which is in particular unavoidable in cases where the filter material is bent around an axis extending in a direction transverse to the folds (because the fold vertex has a greater distance to the bending axis than to the fold base).
It is the object of the present invention to provide a filter material laid in folds which shows improved flexibility.
This object is achieved by a filter material formed by bending and laid in a plurality of folds and with said folds provided with at least one bending portion having a bending resistance moment that is reduced in comparison with the remaining portions. The flexibility of the fold material is improved through the arrangement of bending portions according to the invention without the filtering effect being deteriorated, with the filter material being also bendable around a bending axis extending in a direction transverse to the extension of the folds, without the folds collapsing.
Particularly efficient bending portions which, in addition, can be produced in a simple manner are obtained by shaping the folds section-wise in an incomplete manner. Such an incomplete fold configuration may be characterized either alternatively or at the same time. The strip-like arrangement of the bending portions in a direction across the folds further facilitates bending of the folds. A particularly preferred layered structure of the filter material layer and of the filter material may also be used.
The filter material of the invention is particularly suited for producing the respirator or breathing mask for personal protection, said mask containing a shell-shaped mask body, a so-called half mask, which covers a wearer""s mouth and nose. A particularly preferred layered structure of said respirator or breathing mask may use the filter material of the invention.
A particularly preferred apparatus for producing the filter material of the invention uses at least two folding rolls arranged at an axial distance relative to one another. The filter material layer can move freely owing to the absence of any support surface within the distance between the partial rolls, so that the desired incomplete fold configuration can be achieved in a particularly simple and reliable manner.